Lord Alfred Douglas was no more than a 'friend' to Oscar Wilde. Lawrence of Arabia 'preferred the society of men'. Such were the delicate veils drawn over the private lives of the famous in less permissive times. Now they are about to be blown away by candid British biographies for the twenty-first century.

The Oxford Dictionary of National Biography, one of the most audacious publishing projects of all time, will become available in September after 12 years of work costing £25 million. Its 60 volumes - enough to fill three and a half metres of shelf space - will contain 60m words that make up 50,000 mini-biographies of the greatest ever Britons.

It will be the first wholesale update since the original Dictionary of National Biography, a grand Victorian enterprise, since supplemented by extra volumes, decade by decade. As well as adding illustrations - 10,000 portraits have been collected - and boasting an online edition, the new dictionary promises to pull no punches in covering everyone from Karl Marx and Jack the Ripper to Bobby Moore and Princess Diana.

Tom Rosenthal, one of 10,000 contributors working for 450 editors, noted: 'The previous, somewhat mealy-mouthed Victorian obituary standards of dealing with personal conduct and sexual matters have been done away with. No more, "he remained a bachelor", or, "he did not marry", if he was in fact an outrageous old queen. If a poet or painter was an inveterate adulterer and drunken wife-beater then this will be indicated, doubtless in decorous prose.'

The original dictionary entry for Oscar Wilde referred to his homosexual lover Lord Alfred Douglas as 'Wilde's friend' and, in describing the playwright's fall from grace, contrived to sidestep the detail of his conviction for gross indecency after soliciting young men for sex. Instead it said: 'Wilde brought, with fatal insolence, an unsuccessful action for criminal libel against the Marquis of Queensberry. In the result he was himself arrested and charged with offences under the Criminal Law Amendment Act, and being found guilty ... was sentenced by Mr Justice Wills to two years' imprisonment with hard labour.'

The biography of T. E. Lawrence, or Lawrence of Arabia - rumoured to be gay or to have developed sado-masochistic tendencies as a result of a male rape - said coyly: 'He preferred the society of men to that of women, with very few exceptions, and had friends in all classes.' Of Lytton Strachey, the homosexual writer and critic, it mused: 'He never married.'

The dead can expect no such circumspection in 2004. 'You aren't necessarily a bad Prime Minister because you've got a complicated sex life,' said Brian Harrison, the editor. 'I don't think Lloyd George's descendants will be uncomfortable at references to his mistress, Frances Stevenson, which weren't in the old dictionary.

'There are more likely to be fresh details the older the person is. With recent subjects you've always got relatives hanging around. In the old dictionary the spouse, usually wife, is confined to a footnote. We now put them higher up, where they belong, encouraging the author to think about the influence they had.'

Dr Tristram Hunt, the historian whose specialisms include the Victorian period, struck a note of caution: 'If a new detail sheds light on the achievement or notoriety of the person, on the reason why they're in the dictionary, then it's of worth. The DNB doesn't need any spin or new angle. It rests on the value of its content and contributors.'

The monumental reference work will cost £7,500, or £6,500 for those who order it before 30 September. The publishers promise: 'As well as rulers, politicians, church leaders, military officers and scholars, there are scientists and doctors, business people and labour leaders, artists and writers; and also sportspeople, murderers, journalists, actors and actresses, deviant clergymen, agnostics, hangmen, campaigners, famously fat men or old women.'

The list includes some who may not have existed and some who definitely did not exist, but who have had a big impact, such as King Arthur, St George, Britannia and Robin Hood.

With 3,000 additions, the proportion of women in the dictionary has risen from 4 to 10 per cent. Harrison said: 'I don't think the total will ever reach 50 per cent. Many women defined themselves as private until recently.

'We have a lot more people who saw themselves as anti-British than in the last edition. We've put in more of the rebels from the 1916 Easter uprising to create a rounded picture of Britain and Ireland as a whole.'